Endothelial Cells Promote Expansion of Long-Term Engrafting Marrow Hematopoietic Stem and Progenitor Cells in Primates.

: Successful expansion of bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs) would benefit many HSPC transplantation and gene therapy/editing applications. However, current expansion technologies have been limited by a loss of multipotency and self-renewal properties ex vivo. We hypothesized that an ex vivo vascular niche would provide prohematopoietic signals to expand HSPCs while maintaining multipotency and self-renewal. To test this hypothesis, BM autologous CD34(+) cells were expanded in endothelial cell (EC) coculture and transplanted in nonhuman primates. CD34(+)C38(-) HSPCs cocultured with ECs expanded up to 17-fold, with a significant increase in hematopoietic colony-forming activity compared with cells cultured with cytokines alone (colony-forming unit-granulocyte-erythroid-macrophage-monocyte; p < .005). BM CD34(+) cells that were transduced with green fluorescent protein lentivirus vector and expanded on ECs engrafted long term with multilineage polyclonal reconstitution. Gene marking was observed in granulocytes, lymphocytes, platelets, and erythrocytes. Whole transcriptome analysis indicated that EC coculture altered the expression profile of 75 genes in the BM CD34(+) cells without impeding the long-term engraftment potential. These findings show that an ex vivo vascular niche is an effective platform for expansion of adult BM HSPCs.

SIGNIFICANCE: Transplantation of gene-corrected bone marrow (BM) blood-producing stem cells could be used to treat hematologic disease. Expansion of genetically corrected stem cells before reinfusion into the patient would improve engraftment, thus providing an effective therapy for genetic diseases. The results of the present study show that BM stem cells grown on endothelial cells engraft at high levels in the monkey. These results show that endothelial cells support stem cell expansion and are safe for use in transplantation studies and could thus be translated for use in the clinic for expansion of modified stem cells in gene therapy applications in patients.